Amorphous diamond is an electrically insulating, inert, transparent allotrope of carbon. This type of diamond is called amorphous because it lacks a long-range ordered structure. Amorphous diamond contains little or no hydrogen and is characterized by extraordinary hardness. By contrast, diamond-like carbon (DLC) is hydrogenated and softer than amorphous diamond. Various properties of amorphous diamond are described by D. R. McKenzie et al. in "Proc. Diamond Films '90, Crans-Montana, Switzerland 1990", in Diamond and Related Materials, Vol. 1, p. 61 (1991).
Amorphous diamond is not well suited for commercial applications because of its high intrinsic stress and poor adhesion properties. After depositing a coating of amorphous diamond on a substrate, the coating expands, but its expansion is limited because it is bound to the substrate. As a result, pressure builds up and creates stress that is known as intrinsic stress. The poor adhesion of amorphous diamond limits the thickness of coatings which may be applied. In addition, the intrinsic stress of thick diamond-like carbon films deposited on a substrate has been shown by C. J. Torng et al. to cause delamination of the film from the substrate (See "Structure and Bonding Studies of the C:N Thin Films Produced by RF Sputtering Method" in J. Mater. Res., Vol. 5, No. 11 p. 2493 (November 1990).)
The effects of incorporating nitrogen into different types of carbon has been reported with varying degrees of success. Franceschini et al. reported on the effects of incorporating nitrogen into hydrogenated carbon thin films in Applied Physics Letters, Vol. 60, No. 26 at pp. 3229-3231 (Jun. 29, 1992). U.S. Pat. No. 5,110,679 to Haller describes the formation of a crystalline carbon nitride by sputtering carbon in the presence of a nitrogen atmosphere onto a single crystal germanium or silicon substrate.
Among the techniques used to prepare diamond films, chemical vapor deposition (CVD) is the most common. However, CVD-produced diamond films often have poor adhesion, excessive (thermally induced) stress and generally require deposition temperatures above 800.degree. C.
Therefore, a method for coating amorphous diamond onto a substrate which overcomes the aforementioned difficulties is highly desirable.